ALGAE. CHLOROPHYCEAE. 37 



each of the three subdivisions which are here distinguished, there are some forms 

 with extremely simple, some with more or less complex vegetative bodies. The three 

 subdivisions are the Chlorophyceae or green Algae, the Phaeophyceae or brown Algae, 

 and the Rhodophyceae or red Algae or Florideae. Here too the appearance in- 

 dicated by the name of these subdivisions, viz. the colouring of the cell-contents, 

 is not the real ground of division, but the fact that in each of these groups we have 

 before us a number of forms, in which the course of development is fundamentally 

 the same, but with a certain amount of variation within the limits of each sub- 

 division. 



All the three groups have chlorophyll-corpuscles ; but in the Chlorophyceae alone 

 the green colour appears pure and unmixed, in the Phaeophyceae it is obscured by a 

 brown, and in the Florideae by a red pigment. 



1. The Rhodophyceae are distinguished by the fact that their male organs of 

 fertilisation are small cells without the power of active movement (spermatia) ; the 

 female organ, the procarp (see p. 7), consists of a receptive portion, the trichogyne, 

 with which the spermatium coalesces, and of a carpogenous portion, the carpogone, 

 which is excited by fertilisation to a process of vegetation, resulting in the formation 

 of carpospores. The asexual organs of propagation, formed usually by division of 

 a mother-cell into four parts (tetraspores], are also non-motile, being unprovided with 

 cilia. The Florideae are for the most part inhabitants of the sea. Sivarm-spores 

 occur as a rule in both the other subdivisions ; the male and female sexual elements 

 (gametes) take also the form of motile cells in the simplest cases; in the higher forms 

 the male gamete at least, the spermatozoid, is a swarming protoplasmic body. 



2. The Phaeophyceae are known by the circumstance that the two cilia in all 

 the swarm-spores are inserted laterally near the base of the pointed extremity. The 

 species are all marine. 



3. The Chlorophyceae have all swarm-spores; but these in some species have 

 two cilia inserted at the tip of the pointed extremity, in others four or a circle of cilia 

 at their colourless anterior extremity, or finally their whole surface is covered with 

 cilia ( Vaucheria). Some species live in fresh, some in salt water. 



A. CHLOROPHYCEAE. 



The Chlorophyceae may be distributed into several series of forms which are at the 

 same time connected with one another in various ways ; such are the Confervoideae 

 with the two connected series of Conjugatae and Characeae, the Protococcaceae, the 

 Volvocineae, and the Siphoneae ; the essential point of distinction between the sub- 

 divisions is the structure of the thallus. The process of fertilisation within each 

 ascends from the isogamous, i.e. the union of two gametes of similar form, to the 

 oogamous, i.e. the coalescence of gametes of dissimilar form ; the oogamous fertilisation 

 is least distinctly marked in the Protococcaceae, where, as in Phyllobium, one small 

 male motile cell coalesces with one larger female cell, the oosphere. In other respects 

 each section has its own characteristic marks. The green colour of the Chloro- 

 phyceae is often changed in those of its cells which are passing through a period of 

 rest, such as the zygospores and oospores, which then become red. The red colour- 

 ing matter represents a modification of the chlorophyll, which Rostaiinski considers 



